将UIScrollView的底部淡入透明

Question

我有一个UIScrollView,我需要将底部淡入淡出,以便它不会突然切断内容.UIScrollView的背景是自定义颜色.这是我到目前为止,但图层显示为白色,而不是自定义颜色.这就是我想要的,但仅限于底层.

:

这是我到目前为止:

maskLayer = [CAGradientLayer layer];

            CGColorRef firstColor = [UIColor colorWithRed:141 green:211 blue:244 alpha:1.0].CGColor;
            CGColorRef secondColor = [UIColor colorWithRed:141 green:211 blue:244 alpha:0.8].CGColor;
            CGColorRef thirdColor = [UIColor colorWithRed:141 green:211 blue:244 alpha:0.2].CGColor;
            CGColorRef fourthColor = [UIColor colorWithRed:141 green:211 blue:244 alpha:0.0].CGColor;

            maskLayer.colors = [NSArray arrayWithObjects:(__bridge id)firstColor, (__bridge id)secondColor, (__bridge id)thirdColor, (__bridge id)fourthColor, nil];
            maskLayer.locations = [NSArray arrayWithObjects:[NSNumber numberWithFloat:0.0],
                                                        [NSNumber numberWithFloat:0.2],
                                                        [NSNumber numberWithFloat:0.8],
                                                        [NSNumber numberWithFloat:1.0], nil];
            maskLayer.frame = CGRectMake(0, 285, self.loginScrollView.frame.size.width, 40);
            maskLayer.anchorPoint = CGPointZero;
            [self.loginScrollView.layer addSublayer:maskLayer];

由于某种原因,图层显示为白色,只有scrollView的一半宽度.

Answer 1

我使用的方法是子类化UIScrollView,并在layoutSubviews方法中创建遮罩层.

这是我的代码,它将UIScrollView背景颜色的顶部和底部淡化为透明:

#import "FadingScrollView.h"
#import <QuartzCore/QuartzCore.h>

static float const fadePercentage = 0.2;

@implementation FadingScrollView

// ...

- (void)layoutSubviews
{
    [super layoutSubviews];

    NSObject * transparent = (NSObject *) [[UIColor colorWithWhite:0 alpha:0] CGColor];
    NSObject * opaque = (NSObject *) [[UIColor colorWithWhite:0 alpha:1] CGColor];

    CALayer * maskLayer = [CALayer layer];
    maskLayer.frame = self.bounds;

    CAGradientLayer * gradientLayer = [CAGradientLayer layer];
    gradientLayer.frame = CGRectMake(self.bounds.origin.x, 0,
                                     self.bounds.size.width, self.bounds.size.height);

    gradientLayer.colors = [NSArray arrayWithObjects: transparent, opaque,
                            opaque, transparent, nil];

    // Set percentage of scrollview that fades at top & bottom
    gradientLayer.locations = [NSArray arrayWithObjects:
                               [NSNumber numberWithFloat:0],
                               [NSNumber numberWithFloat:fadePercentage],
                               [NSNumber numberWithFloat:1.0 - fadePercentage],
                               [NSNumber numberWithFloat:1], nil];

    [maskLayer addSublayer:gradientLayer];
    self.layer.mask = maskLayer;
}

@end

如果您只想淡化底部,请更改此行:

// Fade bottom of scrollview only
gradientLayer.locations = [NSArray arrayWithObjects:
                           [NSNumber numberWithFloat:0],
                           [NSNumber numberWithFloat:0],
                           [NSNumber numberWithFloat:1.0 - fadePercentage],
                           [NSNumber numberWithFloat:1], nil];

当我自己实现这个时,我发现这个SO问题很有用,而且这个要点在github上.

编辑:我已将此代码放在github上,请参阅此处.

Answer 2

真的很喜欢Steph Sharp的实现,我把它转换成swift并且认为我会分享以防其他人需要它.

let fadePercentage = CGFloat(0.2)

override func layoutSubviews() {

    super.layoutSubviews()

    var transparent = UIColor.clearColor().CGColor
    var opaque = UIColor.blackColor().CGColor

    var maskLayer = CALayer()
    maskLayer.frame = self.bounds

    var gradientLayer = CAGradientLayer()
    gradientLayer.frame = CGRectMake(self.bounds.origin.x, 0, self.bounds.size.width, self.bounds.size.height)
    gradientLayer.colors = [transparent, opaque, opaque, transparent]
    gradientLayer.locations = [0, fadePercentage, 1 - fadePercentage, 1]

    maskLayer.addSublayer(gradientLayer)
    self.layer.mask = maskLayer

}

Answer 3

这是斯蒂芬回答的 swift 3 版本：

let fadePercentage: Double = 0.2

override func layoutSubviews() {

    super.layoutSubviews()

    let transparent = UIColor.clear.cgColor
    let opaque = UIColor.black.cgColor

    let maskLayer = CALayer()
    maskLayer.frame = self.bounds

    let gradientLayer = CAGradientLayer()
    gradientLayer.frame = CGRect(x: self.bounds.origin.x, y: 0, width: self.bounds.size.width, height: self.bounds.size.height)
    gradientLayer.colors = [transparent, opaque, opaque, transparent]
    gradientLayer.locations = [0, NSNumber(floatLiteral: fadePercentage), NSNumber(floatLiteral: 1 - fadePercentage), 1]

    maskLayer.addSublayer(gradientLayer)
    self.layer.mask = maskLayer

}